1. Field of the Invention
The present invention relates to an automatic feeding apparatus of packaging strap for use in an automatic packaging machine and more particularly to an automatic strap feeding apparatus having a control mechanism for determining the amount of strap consumed during every packing operation to control the feeding of an amount of strap prior to each packing operation equal to the amount consumed during the previous packing operation.
2. Description of the Prior Art
Prevalently used automatic packaging machines are of the type in which the arched frame for guiding the packaging strap is provided above the operation table where the package to be strapped is placed and strapping is made around the package to be strapped placed inside said arched frame.
Said arch type automatic packaging machine is characterized in that the feeding roller for feeding the packaging strap to the strap guide track inside said arch is equipped and the strap is fed to the inside of the arch by forwardly rotating said feed roller and by reversely rotating said feed roller, winding the strap around the package to be strapped and tightening are made. This type of automatic packaging machine is generally called feed out type.
Strap feeding means of feed out type in the early stage comprises a pair of forward and reverse rotation feed rolls by which the packaging strap is pulled out directly from the strap reel and rewinding is made. Therefore owing to the inertia of the strap reel, the speed of the strap feeding is decreased and the deformation of plastic strap is caused by its curve, twist or buckling. Furthermore rewinding for tightening the strap is extremely difficult. In order to overcome these disadvantages in said early means, the means generally called prefeeding type was developed.
With reference to FIG. 8 which shows a typical example of the prefeed type, it is characterized in that the strap amount detecting means comprising prefeed roller 6, strap pool 9, movable plate 35 and limit switch 34 as well as feed roller 3 is provided and when the extra loosening of the strap inside the strap pool is disappeared, the strap is always replenished by the prefeed roller regardless of the consumption amount of strap. By this the feeding speed of strap can be increased, but there was caused the new disadvantage that the strap amount accommodated inside the strap pool is not maintained constant and since operation is carried out so that the strap is always supplied to the inside of the pool, the curving tendency of packaging strap made of plastic material is caused when the packaging machine is not in operation.